Try removing oldest sessions instead of maintaining max size 2

org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/cli/services/ExplicitExpirySessionCacheDecorator.java

@@ -37,15 +37,6 @@ public class ExplicitExpirySessionCacheDecorator implements SessionCache {
     return key;
   }
 
-  @Override
-  public String cacheSession(Supplier<ValidationEngine> validationEngineSupplier) {
-    maintainSessionIds(null);
-    ValidationEngine validationEngine = validationEngineSupplier.get();
-    String key = sessionCache.cacheSession(validationEngine);
-    sessionIds.add(key);
-    return key;
-  }
-
   private void maintainSessionIds(String keyToAdd) {
     if (keyToAdd != null || sessionCache.sessionExists(keyToAdd)) {
       return;

org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/cli/services/PassiveExpiringSessionCache.java

@@ -45,12 +45,6 @@ public class PassiveExpiringSessionCache implements SessionCache {
     return generatedId;
   }
 
-  @Override
-  public String cacheSession(Supplier<ValidationEngine> validationEngineSupplier) {
-    ValidationEngine engine = validationEngineSupplier.get();
-    return this.cacheSession(engine);
-  }
-
   /**
    * Stores the initialized {@link ValidationEngine} in the cache with the passed in id as the key. If a null key is
    * passed in, a new key is generated and returned.

org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/cli/services/SessionCache.java

@@ -15,14 +15,6 @@ public interface SessionCache {
    */
   String cacheSession(ValidationEngine validationEngine);
 
-  /**
-   * Uses the passed  {@link Supplier} to generate a {@link ValidationEngine} and add it to the cache. Returns the
-   * session id that will be associated with the generated instance.
-   * @param validationEngineSupplier {@link Supplier} of {@link ValidationEngine}
-   * @return The {@link String} id associated with the stored instance.
-   */
-  String cacheSession(Supplier<ValidationEngine> validationEngineSupplier);
-
   /**
    * Stores the initialized {@link ValidationEngine} in the cache with the passed in id as the key. If a null key is
    * passed in, a new key is generated and returned.

org.hl7.fhir.validation/src/main/java/org/hl7/fhir/validation/cli/services/ValidationService.java

@@ -490,19 +490,10 @@ public class ValidationService {
         System.out.println("No such cached session exists for session id " + sessionId + ", re-instantiating validator.");
       }
 
-      // Send a supplier instead of instantiating. This will permit the sessionCache to manage existing sessions (drop
+      ValidationEngine validationEngine = getValidationEngineFromCliContext(cliContext, definitions, tt);
-      // or expire old sessions as needed)
+      sessionId = sessionCache.cacheSession(validationEngine);
-      sessionId = sessionCache.cacheSession(() -> {
+      System.out.println("Cached new session. Cache size = " + sessionCache.getSessionIds().size());
 
-        try {
-          return buildValidationEngine(cliContext, definitions, tt);
-        } catch (IOException e) {
-          throw new RuntimeException(e);
-        } catch (URISyntaxException e) {
-          throw new RuntimeException(e);
-        }
-
-      });
     } else {
       System.out.println("Cached session exists for session id " + sessionId + ", returning stored validator session id. Cache size = " + sessionCache.getSessionIds().size());
     }

org.hl7.fhir.validation/src/test/java/org/hl7/fhir/validation/cli/services/ExplicitExpirySessionCacheDecoratorTest.java

@@ -11,7 +11,7 @@ import java.util.ArrayList;
 
 import static org.mockito.Mockito.mock;
 
-public class MaxSizeSessionCacheDecoratorTest {
+public class ExplicitExpirySessionCacheDecoratorTest {
 
   private List<ValidationEngine> getMockedEngines(int count) {
     List<ValidationEngine> engines = new ArrayList<>();
@@ -71,17 +71,6 @@ public class MaxSizeSessionCacheDecoratorTest {
     Assertions.assertFalse(sessionCache.expireOldestSession());
   }
 
-  @Test
-  public void producerAddTest() {
-    ExplicitExpirySessionCacheDecorator maxSizeSessionCacheDecorator = new ExplicitExpirySessionCacheDecorator(new PassiveExpiringSessionCache());
-    ValidationEngine producedEngine = mock(ValidationEngine.class);
-    String sessionId = maxSizeSessionCacheDecorator.cacheSession(() -> {
-      return producedEngine;
-    });
-    Assertions.assertEquals(1, maxSizeSessionCacheDecorator.getSessionIds().size());
-    Assertions.assertSame(producedEngine, maxSizeSessionCacheDecorator.fetchSessionValidatorEngine(sessionId));
-  }
-
   private String getKeyByIndex(LinkedHashMap<String, ValidationEngine> engineMap, int index) {
     return (String) engineMap.keySet().toArray()[index];
   }